fuel book docs for project.metadata section

docs/book/src/forc/manifest_reference.md

@@ -11,6 +11,7 @@ The `Forc.toml` (the _manifest_ file) is a compulsory file for each package and
     * For the recommended way of selecting an entry point of large libraries please take a look at: [Libraries](./../sway-program-types/libraries.md)
   * `implicit-std` -  Controls whether provided `std` version (with the current `forc` version) will get added as a dependency _implicitly_. _Unless you know what you are doing, leave this as default._
   * `forc-version` - The minimum forc version required for this project to work properly.
+  * `metadata` - Metadata for the project; can be used by tools which would like to store package configuration in `Forc.toml`.
 
 * [`[dependencies]`](#the-dependencies-section) — Defines the dependencies.
 * `[network]` — Defines a network for forc to interact with.
@@ -41,6 +42,9 @@ entry = "main.sw"
 organization = "Fuel_Labs"
 license = "Apache-2.0"
 name = "wallet_contract"
+
+[project.metadata]
+indexing = { namespace = "counter-contract", schema_path = "out/release/counter-contract-abi.json" }
 ```
 
 ## The `[dependencies]` section